I've e-mailed Tom Z. a few times. He seems knowledgable and helpful.He sells three versions; the Dakini (original Z-horn) that uses 4 inch drivers; a Heruka that uses a 6 inch Fostex FE168E Sigma driver; and a larger one yet, the Garuda, that uses the Fostex FE206e. He's told me that he really doesn't care for the FE206e, but offers it to those who want it. The Heruka has more solid bass/mids than the , but reportedly gets "soft" on the high end.
Each design is a floorstanding, rear horn loaded cabinet with front firing mouth. The Dakini can be fitted with 4 different 4 inch drivers. I like having driver options, offers different cabinet materials, and that he freely offers the cabinet plans. Tom is considering adding some sort of larger baffle piece to reduce baffle step loss.
Some would argue front firing versus rear firing horns, but the audible differences are rather small and like most everything else there are trade-offs for both. Rear firing can use the back wall/corner to reinforcement bass output, but delays the signal coming from the horn more than a front firing cabinet. Remember that at best these designs only boost an octave or so.